PK23-2, a line of six-rowed barley (Hordeum vulgare L.) originating from Pakistan, has resistance to Japanese strains I and III of the barley yellow mosaic virus (BaYMV). To identify the source of resistance in this line, reciprocal crosses were made between the susceptible cultivar Daisen-gold and PK23-2. Genetic analyses in the F(1) generation, F(2) generation, and a doubled haploid population (DH45) derived from the F(1) revealed that PK23-2 harbors one dominant and one recessive resistance genes. A linkage map was constructed using 61 lines of DH45 and 127 DNA markers; this map covered 1268.8 cM in 10 linkage groups. One QTL having a LOD score of 4.07 and explaining 26.8% of the phenotypic variance explained (PVE) for resistance to BaYMV was detected at DNA marker ABG070 on chromosome 3H. Another QTL having a LOD score of 3.53 and PVE of 27.2% was located at marker Bmag0490 on chromosome 4H. The resistance gene on chromosome 3H, here named Rym17, showed dominant inheritance, whereas the gene on chromosome 4H, here named rym18, showed recessive inheritance in F(1) populations derived from crosses between several resistant lines of DH45 and Daisen-gold. The BaYMV recessive resistance genes rym1, rym3, and rym5, found in Japanese barley germplasm, were not allelic to rym18. These results revealed that PK23-2 harbors two previously unidentified resistance genes, Rym17 on 3H and rym18 on 4H; Rym17 is the first dominant BaYMV resistance gene to be identified in primary gene pool. These new genes, particularly dominant Rym17, represent a potentially valuable genetic resource against BaYMV disease.

This study was conducted to select a DNA marker linked to the new recessive resistance gene rym7t, which is derived from 'Tokushima mochihadaka' and confers resistance to Barley yellow mosaic virus (BaYMV) strains I, II and III. A genetic linkage map neighboring rym7t was constructed using doubled haploid lines derived from a cross between the resistant parent 'DH21-73,' which includes rym7t, and susceptible parent 'Haruna Nijo'. Two SSR markers, Bmac0031 and Bamc0167 were selected, adjacent to each side of the rym7t locus. The genotype of the two SSR markers corresponded well to the phenotype of BaYMV resistance. The field test of Barley yellow mosaic disease (virus strain I) resistance of F 2 individuals derived from a cross between the susceptible parent 'New Golden' and resistant parent 'DH42-84,' which includes rym7t, showed that the correspondence rates between phenotypes of BaYMV resistance and genotypes with Bmac0031 and Bamc0167 were 98.6% and 98.8%, respectively. In the case of correspondence between the two markers' genotypes, they corresponded exactly with the phenotype of BaYMV resistance of F 2 individuals. The two SSR markers were co-dominant, so both could clearly identify susceptible plants with heterozygous rym7t. The two SSR markers could be useful for marker-assisted selection of resistant lines including rym7t.

To establish a Marker Assisted Selection (MAS) system for lines with a low occurrence of hull-cracked grain in malting barley, we screened about 1,000 DNA markers to detect polymorphisms between Kinuyutaka (low occurrence of hull-cracked grain) and Yoshikei 15 (high occurrence of hull-cracked grain). Then, we constructed a genetic map for Kinuyutaka × Yoshikei 15 using 150 doubled haploid lines (DHLs) with 55 polymorphic DNA markers. This map covered 546.8 cM and eight linkage groups on seven barley chromosomes. The QTL analyses revealed three QTLs for the hull-cracked grain on barley chromosomes 2H, 3H and 6H. These DNA markers on three QTLs are important for selecting tolerant lines for hull-cracked grain.

No abstract

To develop a DNA marker assisted selection system for lines with recessive resistance gene to all races of barley yellow mosaic virus (BaYMV), we produced doubled haploid lines (DHLs) of barley (Hordeum vulgare L.) by the bulbosum method. Japanese six-rowed barley cultivar Shimakei 6 with a gene for resistance to all races of BaYMV was crossed with susceptible two-rowed barley cultivar lk2. DHLs were obtained by pollinating the F 1 plants with pollen of H.bulbosum L.. Frequency of DHLs obtained was 4.5% of the pollinated fl orets. Ninety fi ve DHLs were classifi ed into 48 resistant and 47 susceptible lines in the fi eld infected with BaYMV strain I. This segregation ratio fi tted a theoretical ratio of 1:1. Segregation ratios determined with 36 molecular markers also fi tted a theoretical ratio of 1:1 except for one marker. No heterozygous genotype was observed. DHLs are useful because we could obtain fi xed lines with a completely homogeneous phenotype in a short period, and reliable repeated evaluation of phenotype is possible because they are fi xed without segregation by seed multiplication.